The search for new therapeutic agents has been improved in recent years by better understanding of the structure of proteins and other biomolecules associated with target diseases. One important class of these proteins are the sigma (σ) receptors, cell surface receptors of the central nervous system (CNS) which may be related to the dysphoric, hallucinogenic and cardiac stimulant effects of opioids. From studies of the biology and function of sigma receptors, evidence has been presented that sigma receptor ligands may be useful in the treatment of psychosis and movement disorders such as dystonia and tardive dyskinesia, and motor disturbances associated with Huntington's chorea or Tourette's syndrome and in Parkinson's disease (Walker, J. M. et al, Pharmacological Reviews, 1990, 42, 355). It has been reported that the known sigma receptor ligand rimcazole clinically shows effects in the treatment of psychosis (Snyder, S. H., Largent, B. L. J. Neuropsychiatry 1989, 1, 7). The sigma binding sites have preferential affinity for the dextrorotatory isomers of certain opiate benzomorphans, such as (+)-SKF-10047, (+)-cyclazocine, and (+)-pentazocine and also for some narcoleptics such as haloperidol.
“The sigma receptor/s” as used in this application is/are well known and defined using the following citation: This binding site represents a typical protein different from opioid, NMDA, dopaminergic, and other known neurotransmitter or hormone receptor families (G. Ronsisvalle et al. Pure Appl. Chem. 73, 1499-1509 (2001)).
The sigma receptor has at least two subtypes, which may be discriminated by different drugs. (+)-SKF-10047 has nanomolar affinity for the sigma 1 (σ1) site, and micromolar affinity for the sigma 2 (σ2) site. Haloperidol has similar affinities for both subtypes.
The σ1 receptor is a chaperone protein expressed in numerous adult mammal tissues (e.g. central nervous system, ovary, testicle, placenta, adrenal gland, spleen, liver, kidney, gastrointestinal tract) as well as in embryo development from its earliest stages, and is apparently involved in a large number of physiological functions. Its high affinity for various pharmaceuticals has been described, such as for (+)-SKF-10047, (+)-pentazocine, haloperidol and rimcazole, among others, known ligands with analgesic, anxiolytic, antidepressive, antiamnesic, antipsychotic and neuroprotective activity. The σ1 receptor is of great interest in pharmacology in view of its possible physiological role in processes related to analgesia, anxiety, addiction, amnesia, depression, schizophrenia, stress, neuroprotection and psychosis [Kaiser et al (1991) Neurotransmissions 7 (1): 1-5], [Walker, J. M. et al, Pharmacological Reviews, 1990, 42, 355] and [Bowen W. D. (2000) Pharmaceutica Acta Helvetiae 74: 211-218].
The σ2 receptor is also expressed in numerous adult mammal tissues (e.g. nervous system, immune system, endocrine system, liver, kidney). σ2 receptors can be components in a new apoptosis route that may play an important role in regulating cell proliferation or in cell development. This route seems to consist of σ2 receptors joined to intracellular membranes, located in organelles storing calcium, such as the endoplasmic reticulum and mitochondria, which also have the ability to release calcium from these organelles. The calcium signals can be used in the signaling route for normal cells and/or in induction of apoptosis.
Agonists of σ2 receptors induce changes in cell morphology, apoptosis in several types of cell lines and regulate the expression of p-glycoprotein mRNA, so that they are potentially useful as antineoplasic agents for treatment of cancer. In fact, σ2 receptor agonists have been observed to induce apoptosis in mammary tumour cell lines resistant to common antineoplasic agents that damage DNA. In addition, agonists of σ2 receptors enhance the cytotoxic effects of these antineoplasic agents at concentrations in which the agonist is not cytotoxic. Thus, agonists of σ2 receptors can be used as antineoplasic agents at doses inducing apoptosis or at sub-toxic doses in combination with other antineoplasic agents to revert the resistance to the drug, thereby allowing using lower doses of the antineoplasic agent and considerably reducing its adverse effects.
Antagonists of σ2 receptors can prevent the irreversible motor side effects caused by typical neuroleptic agents. In fact, it has been found that antagonists of σ2 receptors can be useful as agents for improving the weakening effects of delayed dyskinesia appearing in patients due to chronic treatment of psychosis with typical antipsychotic drugs, such as haloperidol. σ2 receptors also seem to play a role in certain degenerative disorders in which blocking these receptors could be useful.
Endogenous sigma ligands are not known, although progesterone has been suggested to be one of them. Possible sigma-site-mediated drug effects include modulation of glutamate receptor function, neurotransmitter response, neuroprotection, behavior, and cognition (Quirion, R. et al. Trends Pharmacol. Sci., 1992, 13:85-86). Most studies have implied that sigma binding sites (receptors) are plasmalemmal elements of the signal transduction cascade. Drugs reported to be selective sigma ligands have been evaluated as antipsychotics (Hanner, M. et al. Proc. Natl. Acad. Sci., 1996, 93:8072-8077). The existence of σ receptors in the CNS, immune and endocrine systems have suggested a likelihood that it may serve as link between the three systems.
In view of the potential therapeutic applications of agonists or antagonists of the a receptor, a great effort has been directed to find selective ligands. Different a receptor ligands have been reported.
For instance, the international patent application WO-2008/055932 deals with 1,2,4-triazole compounds having good activity towards a receptors. WO-2009/071657 also reports tricyclic triazolic compounds having good activity towards a receptors. Pyrazoles compounds have been described in the international application WO-2011/147910 as σreceptor inhibitors.
Some fused compounds have also been reported as a ligands. For instance the pyrazolo[3,4-d]pyrimidine disclosed in the international application WO-2013/010950, as well as the pyrazolo[1,5-a]pyridines described in WO-2013/124341.
Nevertheless, there is still a need to find compounds having pharmacological activity towards the σreceptor, being both effective and selective, and having good “drugability” properties, i.e. good pharmaceutical properties related to administration, distribution, metabolism and excretion.